Abstract: Dendritic cells (DCs) reside at the interface of innate and adaptive immunity. They can capture antigens, internalize and degrade them, and present antigen-derived peptides to T cells. The signals generated in these steps result in the release of cytokines that shape T cell responses. Due to their roles as critical antigen-presenting cells, DCs are covered with receptors capable of internalizing antigens?especially lectins. The transmembrane lectins on the DC surface can bind and internalize glycosylated antigens to influence DC signaling and the cytokines that drive the differentiation of T cell subsets. As a result, lectins could be exploited to direct vaccines to dendritic cells and to tailor the immune responses they elicit. The goal of this project is to develop an understanding of key DC lectins to capitalize on this potential. Aim 1 focuses on understanding the combinatorics of lectin engagement and signaling. We hypothesize that glycans that can bind the toll-like receptors and lectins will bias DC signaling and therefore T cell responses. We propose to identify candidate glycans with these properties by assessing the selectivity of DC lectins (DC-SIGN, MGL, dectin-1, dectin-2) for microbial glycans using glycan arrays. We also will synthesize ligands that can bridge DC lectins and TLRs to examine the impact of dual engagement directly. In Aim 2, we shall evaluate the hypothesis that the DC lectins function as mechanosensors. Our preliminary results with DC-SIGN suggest that particulate antigens and soluble antigens differ in their trafficking. These data suggest that DC-SIGN can detect differences in stiffness. Pathogens (e.g., viruses, bacteria, fungi) are much stiffer than human cells, so antigen mechanosensing may be a means of distinguishing foreign from self. Understanding how antigen stiffness influences lectin and TLR signaling could lead to new strategies to modulate immunity. In Aim 3, we examine immune responses to antigens that target DC lectins and TLRs in vivo. The proposed experiments leverage our expertise in chemical biology to test novel hypotheses regarding the signaling pathways and molecular mechanisms that underlie how DCs shape T cell responses and, therefore, immunity. Progress on the proposed Aims is designed to yield new strategies to recruit the immune system to treat human disease.